The present invention relates to a small self-propelled loader which has hydraulically powered drive and work elements, connected in a hydraulic system to provide desired operational functions utilizing the available horsepower efficiently. The engines on small loaders are also relatively low horsepower, and by using the hydraulic power available efficiently, various tasks can be carried out at the same time that the loader can be moved or driven at an appropriate speed.
Various small loaders have been advanced, and these usually do use an internal combustion engine with hydraulic drives for the propulsion system, as well as hydraulic cylinders for moving loader arms and driving attachments or accessories. These loaders generally do not have an operator""s compartment, but the operator will stand on a platform, or on the ground, adjacent to controls at the rear of the loader. In order to efficiently use available power, it is desirable to have the full flow of hydraulic pumps available for propelling the vehicle at times, and at other times it is desirable to use a high pressure for accessories while permitting the vehicle to creep at a slow speed, for example when operating a trencher. The present hydraulic system is connected using standard components to achieve the desired results.
The present invention relates to a hydraulic system for a small loader, as shown a track driven loader propelled by hydraulic motors. The internal combustion engine that is used is maintained at a small size and horsepower output based on the tasks involved. The loader is completely hydraulically driven and operated.
The loader of the present invention uses tandem gear pumps that can be controlled in various modes of operation. When maximum travel speed is desired, separate pump sections are connected to drive the hydraulic motors on the opposite sides of the loader or vehicle, so that each of the motors is receiving the full flow from one of the pump sections or separate pump.
A circuit is provided for carrying the flow of hydraulic fluid under pressure beyond the motors in one mode. The motor valves have a flow through center position where the flow enters a common drain line. The return side of the motors is also connected to the common line leading to a diverter valve and then to a work motor group valve, such as hydraulic lift cylinders for loader arms, a tilt cylinder for a loader bucket, and to auxiliary connections for driving hydraulic motors or actuators on attachments that are used with the loader. Excess flow then is returned to the reservoir or tank, after it has been passed through the necessary valves for controlling the work motor components.
Additionally, the hydraulic circuit is made so that when it is desired to direct the flow from the pumps primarily to work group motors, for example when the loader may be standing still or as will be explained when it is to move only at a very low or xe2x80x9ccreepxe2x80x9d speed, the diverter valve can be operated to direct the primary flow from the pumps to the work group valve, so that substantially the full output of one pump, and, if desired, part of the output from the other pump can be used for operating work motors such as the loader lift cylinders or actuators, the tilt cylinder, or some rotary motors for auxiliary equipment connected through quick couplers that connect hydraulic components on attachments to lines on the loader.
The hydraulic system includes a flow control valve that is manually adjustable when the diverter valve is directing the major flow from the pump sections to the work group valve to permit a controlled amount of hydraulic fluid under pressure from one pump section to be divided and supplied to the valves for the drive or travel motors. The low, controlled flow to the respective drive motors permits a xe2x80x9ccreepxe2x80x9d movement while the majority of the flow powers an attachment motor, such as a trencher or other component that requires some forward motion of the loader at the same time that the auxiliary attachment is working.
The hydraulic system provides efficiency of operation based on the available power.